The propagation speed (simply referred to as “sound speed”) of an ultrasonic wave differs with the diagnostic target part of the subject. In an ultrasonic diagnostic apparatus in the related art, an examiner, such as a doctor or a clinical laboratory technician, can set the sound speed for every target part.
In addition, even if the target part (for example, the liver) is the same, there is a problem in that the sound speed of a received ultrasonic wave in the case of a subject suffering from liver cirrhosis is faster than that in the case of a healthy subject.
Therefore, in PTL 1, a transmission focus generating circuit performs transmission focusing according to the transmission focus pattern which is sequentially selected by a focus pattern selection circuit. A receiving focus generating circuit performs receiving focusing for an echo signal according to the receiving focus pattern corresponding to the transmission focus pattern, and a plurality of image data items with different focus patterns for the same part of the subject are stored in a plurality of memories.
A focus evaluation circuit selects image data in the optimal focus condition by comparing predetermined characteristic amounts of the plurality of image data items stored in the plurality of memories, stores the selected image data in a combination memory, and combines tomographic images. Thus, an ultrasonic diagnostic apparatus has been proposed which always acquires an image in the optimal focus condition regardless of variations in conditions, such as distribution of the sound speed within the subject, and without artificial means.